NEW YORK (AP) — The Food and Drug Administration on Thursday advised patients who have heart devices that include several types of wires made by St. Jude Medical Inc. to have an X-ray or another type of scan to test the wire's insulation.

The FDA is recommending the scans for patients who have implantable heart devices with Riata or Riata ST wires. It says the scans are needed to detect potential problems with the insulation. The wires, which are called leads, attach a defibrillator to a patient's heart. The defibrillators are lifesaving devices implanted in the chest to correct dangerous heart rhythms that can be fatal. They monitor the heart for irregular beats, occasionally triggering electrical shocks that correct the problem.

However if the insulation is eroded, there is a greater chance the device could malfunction and either deliver a shock when none is needed, or fail to shock the patient's heart when it is not beating properly. The FDA said the scans could reveal abnormalities with the insulation, but it is not recommending that all patients have the wires removed. It said that decision should be made after careful consideration of the risks and benefits for each patient.

St. Jude stopped selling the Riata wires in late 2010 because of concerns about the insulation, and it recalled the devices in late 2011. Earlier this year the company recalled two other wires, QuickSite and QuickFlex. Around 79,000 Riata leads are implanted in U.S. patients, and the FDA ordered St. Jude to conduct a three-year study to learn more about the risk of insulation failure.

The FDA said most of the devices are functioning normally, but that more information is needed.

"The agency does not have enough information to determine the frequency and timing of insulation failure in these leads," said Jeffrey Shuren, director of the FDA's Center for Devices and Radiological Health. "Therefore, the post market surveillance studies will ensure that health care professionals and patients get the data they need to better guide clinical management decisions."

St. Jude is being ordered to collect data on patients with Riata and Riata ST, QuickSite and QuickFlex, and its Optim and Durata leads. Durata is a newer wire that is insulated with polyurethane, and St. Jude has said it is not susceptible to the problems that affect Riata wires, which are coated with silicone. St. Jude has not disclosed insulation problems with Durata

However Jefferies & Co. analyst Raj Denhoy said the news could still hurt Durata sales, writing that the news could reduce physicians' confidence in the product. He said they may choose other wires with longer safety records.

In July a law firm started a class action lawsuit against the St. Paul, Minn., company, saying St. Jude did not tell shareholders the full extent of the problems with the products.

Shares of St. Jude Medical lost $1.69, or 4.4 percent, to $26.87 on Thursday.